fix typos and build warning

- correct some double backslashes
- correct wrong indentation
- correct missing backtick
rephrase sentence on Xml::build()
Merge pull request #1718 from antograssiot/3.0

3.0 fix typos and build warning
finish review of fr cakephp-overview
[fr] review of cakephp-overview
[fr] fix typo
[fr] change en links with fr links in what-is-cakephp
Merge pull request #1720 from cakephp/3.0-fr-overview

3.0 [fr] overview chapter
fix sphinx warnings
continue to fix sphinx warnings
update fr migration guide
ends review of appendices
minor corrections

- fix typos
-format configuration chapter
Merge pull request #1724 from cakephp/3.0-small-updates

3.0 - minor corrections
[fr] - review migration guide
[fr] review orm migration
Merge pull request #1727 from cakephp/3.0-fr-appendices

3.0 [fr] appendices translation
[fr] small fix in appendices
Merge pull request #1728 from cakephp/3.0-fr-sphinx-corrections

3.0 fr sphinx corrections